'The idea that novels are going to teach you anything is perhaps a bit far-fetched. In a way, I think the novel is over." For someone who, over a period of 40 years, has written more than 30 novels, flippantly proclaiming that the medium is dead might be a cause for concern. Not least for her publishers.

But this is Fay Weldon. Never one to shy away from big proclamations, she will, seemingly from nowhere and matter-of-factly make off-the-cuff claims, quickly followed by a wry smile or mischievous chuckle. She did, after all, as an advertising copywriter in the 1960s, come up the slogan "Vodka gets you drunker quicker", delivered to her superiors, one would imagine, with just a slightly raised eyebrow.

Now here she is, aged 80, embarking on a trilogy of historical novels. The first, Habits of the House, is published this week. When I meet her in the large house that she shares with her third husband, Nick, on a rare sunny afternoon in Dorset, she tells me with great relief that she just finished the second instalment that morning. So the novel is definitely dead then, is it?

"Well, I wrote the first one and then the publishers said, 'Can we have two more of these please?' which is very flattering, of course."

"You see, novels were once the only way you had of knowing what life was like outside your own family. But now, in the therapist's world, you know all this anyway, because you read in women's magazines about everyday lives."

She adds that writers are now so subservient to the market. Then I notice on her kitchen table a round sticker on an advance copy of her new book: "If you liked Downton Abbey, you'll love this."

Habits of the House sees Weldon return to the territory in which she originally made her name. In the early Seventies, she wrote the first episode of the hit Edwardian drama Upstairs, Downstairs. Her new novel takes places a few years before, at the end of the 19th century, and gently follows, for a period of three months, the lives of those sharing an aristocratic household – both the upstairs and the downstairs, if you will.

Much as in that other popular televised period drama of more recent times [which she hasn't yet seen, she says], times are changing fast. The household learns at the beginning of the novel that its fortune is lost. Soon, the servants begin to gossip and the Earl of Dilberne, a prolific gambler, looks to the US and the O'Brien family, who see the Earl's daughter Minnie as a suitable match for their son, Viscount Arthur.

The plot unfolds with a director's eye as much as a writer's: "It is written very much like a screenplay. It seems a perfectly valid way to write. You don't do it because it's a screenplay, but just because I think audiences are so used to screenplays that they expect novels to unfold in the same kind of way – the setting, the scene, the action, then something happening, and on to the next."

So why a historical novel?

"Well, I just liked the time for various reasons. Having done Upstairs, Downstairs one knew quite a lot about it. A lot of my fictional reading has always been of this era – Edith Wharton or H G Wells."

At this point, as she talks about the benefits of internet research, she matter-of-factly drops into the conversation that she's involved in a copyright claim against some US universities, who are alleged to have acquired unauthorised digital scans of her (and other authors') books from Google. "They've just stolen the copyright. And if you object, their response is, 'well we don't care, we're going to put these books on for the sake of literature'..." Weldon says that she finds all of this "very flattering, but …"

"Also, it's not just that people want them [historical novels]: writing in the present is so difficult because everything changes so fast – attitudes change so fast. What you can write one week, you might not be able to write the next without upsetting the entire country. That's why you're safer back in the past."

Upsetting the entire country is something for which Weldon has form. Back in the late Nineties, a media furore erupted over comments that Weldon had made to the Radio Times about rape not being the worst thing that can happen to a woman. And this from someone who is often described as feminist author. Over a decade later, Weldon shares her latest theory (which is predictably surprising) about that episode, laying the blame squarely at the door of New Labour: "Oddly, in that instance, I think I was framed, really, by the Labour Party because I'd written something in America which got picked up in The Mirror; journalists saw it as a direct attack on Tony Blair so they [the Labour Party] decided to discredit me. Which they did to quite a few people at that particular time."

She says that the quotes were taken out of context, and suddenly appears regretful: "But there's not much you can do about it. It can damage you and make writers much more fearful than they need be. I don't know … everyone is so self-censored now it's hard to tell."

Then that sparkle returns and with a chuckle: "I rang up Germaine [Greer] at the time and she said 'Well, it's only a penis,' which was very comforting!"

Born in 1931 in Birmingham to a literary family, Weldon spent her early years in New Zealand where her father worked as a doctor. If she started her professional career as a television writer, then she learnt her craft as a copywriter. Often compared to the real life woman who inspired Peggy Olsen in TV's Mad Men (a secretary who battled sexism in a chauvinistic, male-dominated world to rise to senior copywriter), Weldon speaks fondly of those times. Was the casual sexism and drinking as terrible as the series portrays it?

"It was exactly like that. But nobody noticed. It didn't matter. There was a whole class of women who liked it, and wanted to work before they got married and settled down to live a boring life. They went off to these offices and ran off with the bosses if they possibly could. Sure, people drank a lot and they had no principles." She then laments: "Now the modern world is so respectful it's almost inhibited. We've become a very … boring lot."

Habits of the House, By Fay Weldon

Head of Zeus £14.99

'"Smithers," said the Countess of Dilberne, "kindly ask Mrs Neville to deduct sixpence from Elsie's wages. His Lordship should have been handed a fresh napkin when he returned to the table." "Yes my Lady," said Smithers. She would of course do no such thing ...'